A card fabrication method is known from US Patent No. WO 2004/074000 wherein data writing is performed by a laser beam after the various layers of the card have been assembled. In order to do this, a specific layer that can be laser written is introduced into the card. This method of writing a text or a pattern is limited and requires a relatively long period of time since the laser beam has to follow a line that matches the desired pattern. This method may be used for personalised card writing. However, it cannot be used for making patterns in different colours or that entirely cover a certain surface of the card. Moreover, this technique requires integration of a specific, laser sensitive layer in the card. Thus, this laser writing technique does not fall within the scope of the present invention, which concerns printing techniques with inks deposited on solid layer or sheet surfaces forming fabricated cards.
With reference to FIG. 1 annexed to this description, we will describe below the conventional method of fabricating electronic cards that have printed patterns with ink on both sides of the card. Three main steps can be differentiated in this conventional method. First of all, an inlay 2 comprising a plurality of electronic modules 4 is formed. Electronic module 4 is formed of a substrate 6 that carries various electronic elements 8, 9 and 10. It will be noted that the electronic module can be of any type and formed for example of electronic elements that are connected to each other without a substrate. Next, two opaque intermediate layers 12 and 13 are provided, on which first and second patterns 14 and 15 are respectively printed. To obtain high quality prints, the intermediate layers are preferably white. Moreover, to ensure that these intermediate layers remain stable during printing of the first and second patterns, those skilled in the art choose for example PVC layers of sufficient thickness, generally more than 100 microns. To obtain a card with high definition prints, in particular an identity card, those skilled in the art choose intermediate layers that preferably have a thickness of between 120 and 150 microns. Finally, two transparent overlays 16 and 17 are placed on the printed patterns and inlay 2, the two intermediate layers 12 and 13 and the two overlays 16 and 17 are placed in a laminating station (represented by the vertical arrows) to assemble the various layers and thus make a plate defining a plurality of printed electronic cards. The individual cards are obtained by finally cutting in the plate.
The thickness of transparent overlays 16 and 17 is generally between 50 and 100 microns, preferably between 60 and 80 microns.
In the usual case of bank cards with a thickness of between 0.76 and 0.84 mm according to the ISO standard, it is noted the total thickness of the intermediate layers and outer protective layers is up to, for example, 360 microns (0.36 millimetres) when intermediate layers with a thickness of 120 microns and outer layers with a thickness of 60 microns are chosen. Thus, to obtain cards within the aforementioned ISO standard, the inlay comprising the electronic units has to have a thickness of less than 480 microns, namely between 400 and 480 microns.
Since the height of inlay 2 is limited, the height of the electronic elements that can be incorporated in inlay 2 is also limited. If the electronic card incorporates at least one electronic element whose height is for example around 300 microns, the thickness of the material forming the inlay is thus thin above and below the electronic element. It will be noted that it is difficult in these conditions to obtain an inlay that has proper flat surfaces and exhibits homogeneous behaviour in the presence of heat. Thus, during the laminating step of the conventional method described above, the intermediate layers will easily experience local deformations in the areas superposed on the electronic elements. The fact that inlay 2 often has surface waviness requires a relatively large supply of thermal energy to reduce this waviness as much as possible during lamination. Compensation for the waviness and deformations of the inlay under the effect of heat generates deformations in the intermediate layers, which, because of their position in the laminated multi-layers, are softened and easily subjected to deformation, or to being spread out slightly. As these intermediate layers actually receive more thermal energy than the inlay and have a smaller thickness than the inlay, they generally experience the most significant deformation. Given that these intermediate layers 12 and 13 carry the printed patterns, it is easy for the patterns to be damaged during the final laminating step.
It will be noted that the local deformations, in the areas where the electronic elements are located, are generated by the different behaviour of the materials forming inlay 2 in the presence of heat, which affects the surface state of the inlay, given the small thickness of said material in these areas when the electronic elements are close to the surfaces of the inlay. Thus, during the laminating step where thermal energy is supplied for assembling the various layers, the behaviour of the material in the areas where the electronic elements are located and any bumps due to the presence of these electronic elements generate small displacements of material in a localised way in the softened intermediate layers, which then causes the printed patterns to be marked on the intermediate layers. Finally, we will also mention the greater hardness of the electronic elements, which mark the intermediate layers just as easily during lamination as they do when the intermediate layers are located at a short distance from the electronic elements.
The conventional fabrication method described above enables the inlay incorporating the electronic units or modules to be made in presses with flat surfaces, thus preventing the electronic units or modules being bent during manufacture of the cards. Those skilled in the art consider this fact to be an essential element in the electronic card fabrication method, particularly when the electronic units or modules have relatively large dimensions and/or electrical connections between various electronic elements. The inlay or central sheet 2 is thus prevented from being bent or cambered during the entire card fabrication method.
Next, those skilled in the art consider the aforementioned conventional method as appropriate for obtaining high quality printing on both sides of the card. The opaque intermediate layers define a flat surface and a homogenous printing support. Moreover, those skilled in the art consider that it is necessary to use these intermediate layers to receive a high definition printed pattern, in particular when they are using a cylinder printing station, especially of the Offset type. Since the printing support is taut over the cylindrical surfaces of the cylinders, those skilled in the art both fabricate the inlay incorporating the electronic elements one the one hand and make a high quality print on a uniform layer entirely formed by a plastic material, for example a PVC sheet on the other hand. Next, these layers are assembled in a laminating station where the layers are pressed between flat surfaces to be assembled.
It is thus observed that those skilled in the art naturally tend to use homogenous plastic sheets, with a thickness of around 100 to 150 microns, as a support for high quality printing, particularly Offset printing. They know that these sheets behave properly in cylinder printing stations. Thus, they separate forming the inlay incorporating the electronic elements and printing on homogenous, flexible supports. Next, they assemble these layers in a flat technique to obtain electronic cards that have printed patterns visible on both sides of the cards. The intermediate layers used as printing support must preferably have a certain thickness to ensure that the support is stable in the printing station and to limit the spreading of these intermediate layers during the subsequent laminating step.
Thus, as already mentioned, the conventional method used by those skilled in the art has a first drawback, due to the limited thickness of inlay 2; which limits the height of the electronic elements incorporated and generates deformations in the printed intermediate layers when they pass into the hot press used to form the finished card.
Other drawbacks of the conventional method described above will be noted in a non-exhaustive manner. Laminating a multi-layer formed of an inlay with a thickness of less than 500 microns, two intermediate layers each with a thickness of less than 100 microns and two transparent outlays with a thickness of 60 to 80 microns requires the use of a relatively expensive laminating station. Moreover, given that inlay 2 may have slight surface waviness and internal stress it the material of which it is formed, laminating the various layers requires good control of card fabrication method, in particular for adjusting the parameters involved in the method, namely the pressure, temperature and length of the laminating cycle. Given the significant know-how necessary for making high quality cards, the laminating step is preferably performed by a specialist in such techniques. It is therefore to be noted that, in addition to the fact that it is very difficult to obtain cards with high definition printed patterns without local deterioration, fabricating these cards must be performed by a specialised manufacturer if one wishes to obtain high quality cards. Thus, flexibility in the finish of the cards, which one might expect from the separate fabrication of inlays incorporating electronic elements and intermediate layers printed in plastic sheet printing stations, cannot be used in practice. Consequently, it is not really possible to envisage, at least in part, performing the printing and final assembly of the cards elsewhere at a distributor's or card user's.